The present invention relates to an actuator assembly for a disc drive, and more specifically to an actuator assembly configured with one or more piezoelectric elements.
Disc drives are data storage devices that preserve digital data in magnetic form on a magnetizable medium. Typically, the magnetizable medium is coated on one or more rigid data discs mounted on a hub of a spindle motor. The spindle motor rotates the discs at a constant high speed as data transducers move radially along the data disc surface reading and writing data. During a write operation, a transducer magnetizes data onto the disc and during a read operation the transducer senses data previously written on the disc. A seek operation refers to the repositioning of the data transducer over a new data location on the disc. In general, each data transducer is mounted on an actuator assembly which moves the transducer to a desired location on the data disc.
Accurate vertical positioning of data transducers over data discs is critical to the operation of a disc drive. If a data transducer is too high above the data disc, for example, the transducer may be unable to detect disc data during a read operation and may be unable to magnetize the data disc during a write operation. Furthermore, decreasing the vertical distance between the transducer and the disc (also known as xe2x80x9cfly heightxe2x80x9d) allows more data to be stored on a disc. However, if the transducer moves too close to the data disc, transducer-disc contact may occur. Transducer-disc contact generally causes debris to deposit on the disc surface and can result in a dreaded disc crash over time. Thus, disc drive manufacturers generally strive to bring the average fly height of data transducers as close as possible to data discs while keeping transducer-disc contact due to fly height errors to an acceptable minimum.
Variations in average transducer fly height from an optimal operating altitude are typically attributed to component manufacturing errors that cumulatively cause the transducer to be positioned either too low or too high from the data disc. Such manufacturing variations and tolerances typically exist for every part on a microscopic level in a disc drive assembly. For example, manufacturing variations in disc spacers, which separate data discs in a multi-disc disc drive, can lead to a sub-optimal average transducer fly height. Similarly, the actuator assembly may be mounted either too low or too high from the data disc.
Besides errors associated with average transducer height, transitory variations in fly height may also cause data errors during a disc drive""s operation. One major cause of inconsistent transducer fly height is minute variations in the data disc""s topography. Data discs are never perfectly flat and contain microscopic peaks and valleys. Such topographical inconsistencies can result in the data transducer flying too far or too near the data disc. Another reason for fly height variations is disc wobble as the disc is rotated about the spindle motor. Imperfections in the spindle motor or disc spacers may lead to unbalanced motion of the discs, thus causing the data discs to wobble back and forth. When disc wobble occurs, the fly height of the data transducer changes as portions of the data disc move closer to the data transducer, while other portions of the data disc move farther away from the data transducer. Along similar lines, the movement of the data discs as a result of vibrations, also referred to as xe2x80x9cdisc flutter,xe2x80x9d can produce transducer fly height variations.
One known actuator structure that helps overcome some causes of transducer fly height variations utilizes an air bearing responsive to changes in fly height. In this arrangement, a flexture is mounted to the end of the actuator arm and pushes the data transducer toward the data disc. The amount of force exerted by the flexture is often referred to as the flexture gram load. Counterbalancing the flexure gram load is the air pressure created between the transducer and data disc when the disc spins rapidly below the transducer. The air pressure acts to lift the transducer away from the disc much like an airplane wing. As a result of these two opposing forces, the data transducer flies over the rotating disc surface at a relatively constant height, rising when the disc surface advances closer to the transducer and falling when the disc surface retreats away from the transducer.
Although an actuator assembly that incorporates the air bearing design described above helps maintain consistent transducer fly height, such an actuator has several shortcomings. Typically, the flexture gram load must fall within tight tolerances for the actuator to properly function. If the gram load is too large, the air pressure created will not be enough to sufficiently lift the transducer over the disc surface. Conversely, if the gram load is too low, the transducer will be lifted too high above the disc surface. As transducers are required to fly ever closer to data discs for increased disc storage capacity, gram load tolerances of conventional air bearing actuators will continue to tighten and actuator flextures meeting such tolerances may become harder to manufacture.
In addition, the air bearing actuator design can create new sources of transducer fly height errors. Since the air bearing design relies on air pressure to counterbalance the flexture gram load and lift the data transducer, factors affecting air pressure between the transducer and the disc also affect the transducer fly height. For example, variations in the operating environment of the disc drive, such as changes in elevation and temperature, can change the air pressure produced between the transducer and the disc, thus altering the transducer fly height. Changes in fly height due to such external factors cannot be easily compensated for during manufacturing and are generally considered inherent to disc drive""s operation. Thus, such external factors may ultimately limit how closely transducers fly above data discs with conventional air bearing assemblies.
Beyond the above-mentioned sources for transducer-disc contact, collisions may also result when an actuator is moved radially across the data disc. For example, as the actuator assembly quickly accelerates and decelerates during seek operations it may twist slightly, causing the data transducer to roll and collide into the disc surface. Moreover, some disc drives employ a transducer parking-ramp to lift the transducer away from the data disc when the drive is not in use. Often times, a transducer edge may catch the data disc surface when the transducer is loaded and unloaded to and from the ramp.
In accordance with the present invention, the above and other problems are solved by providing a piezoelectric assembly in an actuator arm for fine-tuning the position of the data transducer. As such, the invention allows for fly height error correction due to both internal and external disc drive factors. In addition, the piezoelectric assembly of the present invention provides fly height feedback for optimal vertical placement of data transducers above the data discs. Furthermore, the invention may be configured to alert users with an early warning of an imminent catastrophic disc crash. The present invention may also be used to compensate for data transducer roll, as well as to make small radial adjustments of the transducer position across a data disc.
Thus, the present invention generally involves an actuator arm for a disc drive having at least one data disc. The actuator arm includes a data transducer coupled with the actuator arm for reading and writing data from and to the data disc. The actuator arm also includes a piezoelectric assembly with at least one piezoelectric element. The piezoelectric element is configured to vertically displace the data transducer when it is energized. The actuator arm further includes an hourglass shaped arm pivot biasing the actuator arm to a rest position.
The piezoelectric assembly may include at least one top piezoelectric element and at least one bottom piezoelectric element. Similarly, the piezoelectric assembly may include at least one left piezoelectric element and at least one right piezoelectric element. Furthermore, the piezoelectric assembly may include a top right piezoelectric element, a top left piezoelectric element, a bottom left piezoelectric element, and a bottom right piezoelectric element.
The piezoelectric assembly may be configured to roll the data transducer in clockwise and counterclockwise direction. The piezoelectric assembly can also be configured to radially displace the data transducer across the data disc.
Another embodiment of the invention is a method of positioning a data transducer for reading and writing data from and to a data disc. The method includes the step of energizing an actuator assembly motor such that the data transducer moves substantially radially across the data disc. The method also includes the step of applying a position signal to at least one piezoelectric element mounted on the actuator arm, and thereby causing the piezoelectric element to vertically displace the data transducer with respect to the data disc in response to the position signal.
The method may further involve the steps of detecting a contact signal from the piezoelectric element and comparing the contact signal to an upper contact limit. If the contact signal is greater than the upper contact limit, the method further involves the step of modifying the position signal to the piezoelectric element until the contact signal is less than the upper contact limit. In addition, the method can include the steps of comparing the contact signal to an lower contact limit and, if the contact signal is less than the lower contact limit, modifying the position signal to the piezoelectric element until the contact signal is greater than the lower contact limit.
Another aspect of the method includes the steps of detecting a contact signal from the piezoelectric element and comparing the contact signal to an imminent failure limit. If the contact signal is greater than the imminent failure limit, the method further involves the step of issuing an imminent failure warning.
Another aspect of the method includes an actuator arm for a disc drive having at least one data disc. The actuator arm includes a data transducer coupled with the actuator arm for reading and writing data from and to the data disc. A piezoelectric assembly including at least one piezoelectric element is configured to vertically displace the data transducer when the piezoelectric element is energized. The piezoelectric assembly provides a contact signal proportional to a rate of contact between the data transducer and the data disc. The actuator arm further includes a servo unit coupled to the piezoelectric assembly, wherein the servo unit is configured to energize the piezoelectric assembly in response to the contact signal such that a feedback loop is formed.
These and various other features as well as advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.